fix(datepicker): export NgbDatepickerNavigateEvent correctly (#3161)
fix(datepicker): export NgbDatepickerNavigateEvent correctly (#3161)

It wasn't exported from `index.ts` -> wasn't available from `@ng-bootstrap/ng-bootstrap`

Fixes #3160
maxokorokov/core,benouat/ng-bootstrap,ng-bootstrap/ng-bootstrap,benouat/ng-bootstrap,maxokorokov/core,fbasso/ng-bootstrap,jnizet/ng-bootstrap,jnizet/ng-bootstrap,jnizet/ng-bootstrap,maxokorokov/core,fbasso/ng-bootstrap,fbasso/ng-bootstrap,fbasso/ng-bootstrap,ng-bootstrap/ng-bootstrap,jnizet/ng-bootstrap,ng-bootstrap/ng-bootstrap,benouat/ng-bootstrap,benouat/ng-bootstrap,maxokorokov/core,ng-bootstrap/ng-bootstrap